Hizbullah had previously threatened to capture Israeli soldiers, but it had limited its attacks to shelling across the border. Yesterday's strike marked the Islamic militia's biggest operation since 2000, when Israel ended its military occupation of southern Lebanon.

Although the seizure of the two Israeli troops in a cross-border attack by Hizbullah fighters early yesterday morning was celebrated with sweets and firecrackers in the Hizbullah-dominated southern Shia suburbs of Beirut, it will be much less welcome elsewhere in Lebanon's fragile political landscape. The attack was almost certainly carried out without any consultation with the Lebanese government, in which Hizbullah holds two cabinet seats, and risks dragging Beirut into an all-out war with Israel.

In an apparent acknowledgement of his critics in Lebanon, Hizbullah's leader, Hassan Nasrullah, told the country's public it was "not the time for discussion and arguing". "I am not asking for your support or help", he said, but nobody should behave in a way to support the enemy. Today we behaved in a patriotic way."

Since the Israeli withdrawal six years ago, Hizbullah, whose name means Party of God, has occupied a unique position in Lebanon. The Shia group is the last armed militia left from the civil war era and last year, for the first time, it joined the Lebanese government. Despite a 2004 UN resolution that ordered all militias in Lebanon to be disarmed, Hizbullah's fighting units have survived intact. Earlier this year, the Lebanese prime minister, Fouad Siniora, a respected Sunni Muslim banker, explicitly gave his government's support to the group, calling it the "resistance", not a militia.

"To me it looks like Hizbullah is trying to divorce itself from Lebanese politics," said Timur Goksel, who was for more than 20 years the UN spokesman in southern Lebanon and who is now an academic in Beirut. "This is not going down well in Lebanon, certainly in Beirut. And it could get serious internally. In Beirut there are a lot of question marks being raised now."

Much will now depend on the Israeli response. Hizbullah is a highly-organised guerrilla force that does not have easily identifiable military positions which could be targeted in an Israeli operation. Instead it operates among a largely supportive population across southern Lebanon and up into the long Beka'a valley, which runs between two mountain ranges along the Syrian border. Thousands of Lebanese expatriates, many of them Shia and from the south, are holidaying in Lebanon and the risk of civilian casualties from any Israeli strike would be high. Two Lebanese civilians were reported killed yesterday and five wounded. An Israeli attack destroyed a bridge along the southern coastline and jets overflew the town of Saida, south of Beirut.